Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Open Peeps - A hand-drawn illustration library.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Control Illustrations - 108 free flat illustrations with customizable characters
Slack - A messaging app for teams who see through the Earth!
DrawKit - MIT licensed SVG illustrations, in 2 styles